Never been a fan of small parties in big CRPG either, but if after two years of people requesting it as an optional mode in EA (you know, that environment that SHOULD be ideal to try things not set in stone) nothing ever came, I think the chances are pretty slim.
It sucks, as 4-men parties are notoriously a thing for tossers who don't know better, but the good news is that it's relatively easy to mod it, if with a couple of caveats.